1. Field of the Invention
The present invention relates to a failure detecting apparatus that detects a failure of a solenoid-operated control valve for use in a vehicle's brake system.
2. Discussion of Related Art
Patent Document 1 (Japanese Patent Application Publication No. 2003-205838) discloses a vehicle's hydraulic brake device including a solenoid-operated control valve, and Patent Document 2 (Japanese Patent No. 2,546,851) discloses a vehicle's hydraulic brake device including a hydraulic chamber, a high-pressure source, a low-pressure source, a first solenoid-operated control valve provided between the hydraulic chamber and the high-pressure source, a second solenoid-operated control valve provided between the hydraulic chamber and the low-pressure source, a pressure switch that can take different states corresponding to a first state in which a hydraulic pressure in the hydraulic chamber is not higher than a reference pressure and a second state in which the pressure in the hydraulic chamber is higher than the reference pressure, and a failure detecting device that detects respective failures of the first and second solenoid-operated control valves based on a change of the state of the pressure switch upon opening or closing of the first solenoid-operated control valve and a change of the state of the pressure switch upon opening or closing of the second solenoid-operated control valve. In the brake device disclosed by Patent Document 2, when the second solenoid-operated control valve is switched from the closed state thereof to the open state thereof, the pressure in the hydraulic chamber should decrease to a value not higher than the reference value; and subsequently, when the second solenoid-operated control valve is switched to the closed state thereof and the first solenoid-operated control valve is switched from the closed state thereof to the open state thereof, then the pressure in the hydraulic chamber should increase to a value higher than the reference value. Therefore, if the state of the pressure switch does not change upon controlling of an electric current supplied to a coil of each of the first and second solenoid-operated control valves, it can be judged that the each solenoid-operated control valve has failed.